a. Field of the Invention
The present invention pertains generally to an electrophysiological device and method for providing energy to biological tissue and, more particularly, to an ablation apparatus with improved contact sensing capabilities.
b. Background Art
Various devices, such as electrode sensors, thermal sensors, ablation electrodes, and the like, may be implanted in catheters inserted into a patient's body (e.g., the patient's heart) for use in a wide variety of medical procedures, including, without limitation, electrophysiological mapping and tissue ablation. It is often desirable to determine the degree of contact between the device being used and the tissue the device is being used on. As used herein, the term “degree of contact” refers not only to the area of contact between the device and tissue, but also to the force being exerted by the device on the tissue (or vice versa).
By way of illustration, sensor output is only meaningful for mapping procedures when the sensors are in sufficient contact with the tissue being mapped. So-called “false signals” received when the sensor is not in good or sufficient contact with the tissue may result in inaccurate mapping of the tissue (e.g., the interior of a patient's heart).
By way of further illustration, it is desirable to control the level of contact between the device and the tissue in order to form ablation lesions, such as may be formed in treatment of cardiac arrhythmia. In particular, it is desirable to maintain a relatively constant level of contact between the ablation electrode and the cardiac tissue in order to elevate tissue temperature to around 50 degrees C. to form lesions in the cardiac tissue via coagulation necrosis. Such lesions change the electrical properties of the cardiac tissue and may lessen or eliminate undesirable atrial fibrillations when formed at specific locations in cardiac tissue. Insufficient contact during the ablation procedure may result in poor lesion formation.
Tissue contact is not always readily determined using conventional fluoroscopy techniques. Instead, the physician may determine tissue contact based on his/her experience maneuvering the catheter. Such experience only comes with time, and may be lost if the physician does not use the catheter on a regular basis. When used inside the heart, the beating heart further complicates matters by making it difficult to assess and maintain sufficient contact with the tissue for a sufficient length of time. If contact with the tissue cannot be properly maintained, the advantages of using the device may not be fully realized.